|In Cataract surgery, the cloudy natural lens is removed from the eye. In most cases, the focusing power of the natural lens is restored by replacing it with a permanent intra ocular lens (IOL) implant. In connection with this, the power of the intra ocular lens should be determined. The method that calculates the IOL power is called as Optical Biometry.
Ophthalmic biometry examinations can be done using an immersion technique, contact technique or using IOL Master. High quality IOL Master–optical biometry mechanism and the other techniques are available at visioncare for this assessment and we are proud to be the first optical company who facilitated A’ scan service to the public without a waiting list.
In Immersion A’ scan biometry, the patients are placed in a supine position on a flat examination table or in a reclining examination chair and a drop of local anesthetic is applied in both eyes. Then a sclera shell is applied on to the eye. The shell is filled with BSS solution. The ultra sound probe is immersed in the solution in the shell 5 to 10 mm away from the cornea. The patient is asked to look with the other eye at a fixation point placed at the ceiling. Attention is then focused on the screen. The shell is applied on the sclera until the probe is properly aligned with the optical axis of the eye and an acceptable A’ scan echogram is displayed on the screen.
When using the contact method, the patient is examined in the selected position and a drop of local anesthetic is installed in both eyes.
The ultra sound probe is aligned with the visual axis and the patient is asked to fixate a light inside the probe. Then the probe is directly touched with cornea to generate the echo spike
It is rapidly becoming apparent that the most accurate way to measure AL is with ‘Carl Zeiss Medtech IOL Master’ using the 4th generation software by immersion biometry. The IOL Master uses light rather than sound to measure axial length. The technology for Al measurement incorporate in this pioneering system is based on the principle of optical biometry partial coherence intertenometry. The IOL master is extremely user friendly because there’s absolutely no contact with the eye. IOL master allows calculating IOL data using standard international biometry formulas and selecting the lens type from a data base.
The most common method of measuring AL is by the applanation (Contact) technique. However unless this is done by a highly skilled technician it tends to produce myopic surprises because of indentation of the cornea.
It is believed that any surgeon who wishes to produce excellent distance vision for patients with accommodating or multi focal lens should switch as soon as possible to the IOL master or immersion biometry for AL measurements. In addition K’reading is best taken from the IOL master or manually.